Fundamental and Technological Aspects of Finishing Balls of Advanced Ceramics, Glasses, and Silicon Using Magnetic Field Assisted Polishing

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This project is on the finishing of balls of advanced ceramics, glasses, and semiconductor material using the magnetic float polishing technology. Conventional finishing of advanced ceramics and glasses by grinding, polishing, lapping generally leads to several defects including large scratches, formation of pits due to the dislodgment of grains, viscous flow of the glassy phase in the case of glass, and surface and subsurface microcracks. These defects affect the properties and performance of these materials and are traditionally removed by subsequent diamond polishing. To address this difficult problem, a "gentle" finishing technology, called the magnetic float polishing was developed (in a recently completed investigation supported by NSF) without the need to use diamond abrasives. Surface finish on the order of 4 nm Ra and 40 nm Rmax with sphericity in the range of 0.25 micrometers were accomplished on Si3N4 balls with a total polishing time of ~ 20 hours. A better understanding of the mechanical and chemo-mechanical actions involved in the polishing of Si3N4 balls has resulted. In this project, the investigators intend to generalize this work to cover other advanced ceramics (balls of different size and number per batch), various glasses, and silicon. Advanced ceramics, such as Si3N4, SiC, Zr02, and Al2O3 are increasing being considered for structural applications of which Si3N4, in specific, is chosen for hybrid ball and roller bearing applications. Similarly, various types of glasses are used for optical applications, such as lenses and recently spherical silicon balls are being considered for micro-electronic applications (instead of silicon wafers). This research would be the first of its kind on the finishing of silicon balls (instead of wafers) by magnetic float polishing. Thus, the finishing technology proposed is expected to address structural, optical, and electronic applications that can have a significant impact on the manufacture of balls for various advanced technology applications.